As opposed to glasses, metals and metal alloys, and to ceramics, polymer materials are relatively permeable to gases and to moisture. The transfer of oxygen across the walls of a receptacle containing a beverage may ultimately cause the oxidation of certain compounds such as vitamins, fatty acids and proteins. Similarly, a loss of flavor and, more generally, a loss of organoleptic properties may result from weak barrier properties of a food container.
Under the very general term of permeability, three mechanisms can be distinguished:                sorption and desorption on the inside walls of the receptacles;        diffusion across the walls of the receptacles;        migration of certain compounds from the polymer material forming the receptacle to the content of this receptacle.        
Techniques for measuring the permeability of polymer materials are usually concerned with sheet materials and can be classed in three categories: measurements at variable pressure, measurements at variable volume, measurements called isostatic and isobaric measurements.
Various instruments for measuring the permeability, whether to oxygen or to carbon dioxide, are available on the market. Thus, in particular, instruments are sold, under the trade name Ox-tran®, for measuring the permeability to oxygen, and are sold under the trade name Permatran® for measuring the permeability to carbon dioxide (cf. for example document U.S. Pat. No. 6,699,320 (column 4, lines 7 to 16)).
In order to investigate the permeation properties of a three-dimensional container made from a flexible material—like PET, for example—in its geometry of use, this container is merely placed in a test gas atmosphere and a stream of carrier gas is circulated inside the container, the outgoing stream being conveyed to a detection and measuring instrument.
However, due in particular to the sorption of oxygen, and to avoid artefacts, it is necessary first to purge the hollow bodies such as bottles, before actually taking the permeability measurement. This first step is called conditioning.
After this conditioning is completed, a steady state is obtained, in which the permeation measurements can be taken.
To reduce the conditioning time, it has been proposed to place the polymer container under vacuum beforehand (see US 2004/0177676), this technique incurring major risks of irremediable deterioration of the container during the measurement.
Conventionally, after conditioning, to measure the permeability to oxygen, air or oxygen is introduced in a continuous stream of a mixture comprising a high proportion of nitrogen and a low proportion of hydrogen (between 0.5% and 5% hydrogen, typically two percent hydrogen in known instruments for measuring permeability to oxygen). This continuous stream is sent at a very low flow rate, about 10 milliliters per minute. The oxygen is removed by the nitrogen, the carrier gas, and the quantity of oxygen is measured by coulometry.
If the polymer material tested has weak barrier properties, air is employed for the measurement.
For materials basically having good or even very good barrier properties, such as in particular PET receptacles coated with amorphous carbon by the use of plasma deposition technologies, such as the technology described in document EP 1 068 032 which has been developed by the applicant, oxygen is employed for the measurement.
For measuring permeability to carbon dioxide, with known measuring instruments, three methods are provided:                a first method called accumulation, for materials having permeability values lower than 55 cc per square meter and per day. In this first method, an infrared sensor compares the signal obtained for a reference quantity of carbon dioxide in a reference cell and the quantity of carbon dioxide which has passed through the polymer material and has accumulated in a measurement cell, having the same volume as the reference cell;        a second method called the dynamic method, employed for polymer materials having permeability values above 50 cc per square meter and per day. In this second method, when the carbon dioxide passes through the polymer material to be tested to pass into a measurement cell, a current value is obtained by the infrared sensor. As this current value changes linearly with time, a steady state condition is obtained and the steady state signal obtained is compared with the signal obtained when a predefined quantity of CO2 is injected into a volume identical to that of the measurement cell;        a third method called the continuous flow method. In this third method, employed for polymer materials having a permeability of between 30 and 10 000 cc per square meter and per day, and if a large number of samples need to be tested, the carbon dioxide passed through the polymer material is mixed with nitrogen, and it is this mixture which passes in front of the infrared sensor. The value obtained is compared to that of a reference.        
Conditioning is a lengthy step, designed to ensure that the test conditions are at equilibrium.
This conditioning time depends on many factors, such as the barrier properties of the polymer material, the thickness of the polymer material, and the temperature.
When the measurement is taken on a bottle, the conditioning time is commensurate with the developed surface area of the bottle as stated in document FR 2 844 596.
It is routine practice for a person skilled in the art for the conditioning time to be about fifteen to twenty hours, which raises numerous practical problems for tracking the measurements. It is moreover not possible, with techniques known today to the applicant, to take more than one measurement per cell and per 24 hours.
It is the object of the invention to provide a conditioning method and installation for a measurement that is far more rapid and yet just as accurate and reliable.